This is a small stand/holder designed for a standard 120mm fan which can be mounted to any surface using screws.

It costs less material than any other stand I found and takes very little time to print.
It also takes up almost no space (mounting holes are under the fan, so mount the stand to the surface first).

Default dimensions:

• Wall thickness = 3.4 mm
• Fan hole d1 = 7mm, d2 = 5mm
• Mounting hole d = 5

It is customizable which means you can change the hole sizes and other parameters.